Scientists may have found a way to reverse some types of permanent hearing damage after managing to regrow tiny hairs inside the inner ears of mice.
When US researchers injected the mice with a drug, codenamed LY411575, it stimulated the creation of new hairs on the mice, a report in the journal Neuron said.
Many hearing problems are caused by damage to the hairs inside the inner ear, which are moved by sound vibrations and send nerve messages to the brain.
The mice in the study, conducted by the Massachusetts Eye and Ear and Harvard Medical School, went from being completely deaf to being able to hear loud sounds such as doors slamming or car traffic.
"It hasn't been possible to regenerate hair cells in adult mammals before," researcher Dr Albert Edge said.
"The significance of this study is that hearing loss is a huge problem affecting 250 million worldwide."
Experts have warned, however, that a treatment for humans could be a long way off.
"It's a really promising development, but it is one which needs to be treated with considerable caution in terms of a human therapy," Prof Dave Moore, from Britain's Institute of Hearing Research, told the BBC.
"There's been a lot of false starts - hair cell regeneration was originally demonstrated in the 1980s and everyone thought it would just be a matter of years."
Author: Emily O'Keefe